Production Method for Sheets of Glass with a Diffuse Finish, and Resulting Sheet of Glass

ABSTRACT

The present invention relates to a process for manufacturing glass sheets with diffuse finish and the resulting glass sheet by this process. The glass sheet is subjected to a series of alternate immersions in acidic solutions and alkaline solutions to remove impurities and waste and to generate a diffuse finish on both sides of the glass sheet. The process generates in the glass sheet in at least one side, a diffuse surface with a peak to valley roughness (Rt) of between 5.8343 μm and 9.3790 μm; an average roughness (Ra) value between 0.8020 μm and 0.9538 μm; an RMS roughness between 0.9653 μm and 1.1917 μm; a solar transmission between 84.8% and 46.50%; a solar reflection between 7.4 and 4.4%; a light transmission between 88.5% and 67.70%; a reflection of light between 6.50% and 5.20%; and UV transmission between 35.60% and 70.20%.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/437,733 filed on Jun. 11, 2019, which is a divisional of U.S. patentapplication Ser. No. 15/322,284, filed on Jun. 27, 2014, now U.S. Pat.No. 10,358,382, issued on Jul. 23, 2019 which is related to the UnitedStates national phase of International Application No. PCT/MX2014/000098filed Jun. 27, 2014, the disclosures of which are hereby incorporated intheir entirety by reference.

FIELD OF THE INVENTION

The present invention shows a manufacturing process for glass sheetswith diffuse finish, and more specifically, to a manufacturing processfor producing a diffuse glass by immersion in acidic solutions modifyingits optical properties and giving it a diffuse finish.

BACKGROUND

Ever since manufacturing a continuous glass sheet over a layer of tinwas in 1959 (float process) was achieved, applications thereof havediversified encompassing many markets; from applications in theconstruction market to its use with complex forms in the automotivemarket.

One of the applications of float glass is the protection of works of artand portraits, along with a frame made of wood or other materials. Theprimary purpose of covering artwork is the physical protection of thesame from factors such as humidity, heat and stains. Glass is also usedbecause it provides good levels of protection from UV rays which canattack the pigments of artwork whose protection is intended andeventually cause discoloration.

However, a common problem that occurs when using flat glass asprotection for works of art is that when a viewer stands before a pieceframed with this material, instead of seeing the work of art, the viewerwill see its own reflection. In order to eliminate this effect caused bylight reflection, several alternatives have been researched and the mostwidespread solution is the use of diffuse flat glass. Now, the way inwhich diffuse flat glass avoids reflections is by treating its surfacewith acidic solutions. This prevents glare by adding irregularities tothe surface.

Generally, in making this diffuse glass, clear flat glass is used due toits high market availability and low cost compared to other glass types.Typical thickness of this glass ranges from 2.0 mm to 2.5 mm.Conventional clear glass with this thickness has a light transmittanceof about 90% and a reflection of 8%. By giving glass an acid treatment,the reflection level is lowered to about 1%.

There is another raw materials option with low contents of iron that hasbeen used in recent years but has a higher cost. The advantages of usingthis type of raw material is that it has a higher light transmission,around 92%, which allows a better perception of the image that is beingprotected. By performing the same acid treatment, it is possible toobtain the same level of reflection that is achieved with conventionalclear glass which is 1%.

There are other options that can be used for the same purpose, althoughthey involve the use of a complex or high-tech process, thereby makingtheir manufacturing cost much higher. One of these options isanti-reflective (AR) glass manufactured by cathode pulverizingtechnology (sputtering).

Because of its cost, this type of glass is normally used for high valueapplications such as monitor screens or windows that are part of displaycases. The most common configurations used in this type of productsconsists of alternating one high refractive index film (e. g. TiO₂) withone of low refractive index (e. g. SiO₂). Generally, the level ofreflection achieved depends on the number of alternating films, wherethe product having lower performance has at least 4 films.

There are other materials that have been used trying to obtain abehavior similar to that of glass but showing a lower light reflection,one of them is acrylic sheet, which has a high light transmission and anoptical quality similar to that of glass. It shows a great advantageagainst glass from a density viewpoint, since acrylic sheet is a verylight material, but it has the disadvantage of being easily scratchedand retains static charge which is detrimental to certain types of art(technique of pastel and charcoal), so it has not been very successfulfor anti-reflective applications.

Moreover, since the 40s attempts have been made to alter the surface ofglass and give it a diffuse appearance by etching. For example, U.S.Pat. No. 2,348,704 (1944) issued to Frederick W. Adams proposes reducingreflection of light coming from a glass surface by using acids. Thisforms a thin film which is an interference between the exposed filmsurface and the glass surface covered by the film. The study describedby Adams consists in treating glass with a strong mineral acid, in thiscase nitric acid 0.5 N in order to remove the basic glass componentsthat are on the surface without attacking the SiO₂. Subsequently, adilute solution of hydrofluoric acid 0.1% by volume is used. It is wellknown nowadays that the use hydrofluoric acid in such low concentrationsentails a long attack time to obtain the anti-reflective characteristicsobtained by Adams, therefore it is not very practical to apply thesefindings in a production process.

U.S. Pat. No. 2,486,431 issued to Frederick H. Nicoll and Ferd E.Williams also describes the use of a solution of 0.5N nitric acid. Flatglass is immersed in this solution to generate a degradation of theglass surface microscopically eliminating planarity of the surface andforming porosity therein. Once this is achieved, the reaction withnitric acid is interrupted to continue flat glass immersion in asolution of hexafluorosilicic acid with concentrations ranging from 0.3to 3.0 moles/liter working at temperatures between 35 and 55° C. Likethe work done by Adams, again the problem of working with very lowconcentration solutions which need to be changed very quickly in aproduction process is presented. This is because each sheet immersed inthe Hexafluorosilicic acid solution weakens the acid concentration,therefore in each batch that is made to obtain diffuse flat glass,adjustments are necessary to immersion times making it an uneconomic andunstable process.

In U.S. Pat. No. 2,461,840 issued to Frederick H. Nicoll, another methodwas explored to obtain diffuse flat glass, whereby it was not necessaryto immerse the flat glass sheet in acid. Nicoll found that hydrofluoricacid vapor can generate a diffuse surface in the flat glass with no needto previously use other mineral acids. To accomplish this purpose, atank with a wax cover was designed where a 1% solution of hydrofluoricacid was placed. This tank in turn was immersed in a larger tank whichcontained water, which was used to control the temperature ofhydrofluoric acid present in the main tank. Subsequently, a flat glasssheet was placed over the main tank, which would be exposed to attackfrom hydrofluoric acid vapor, generating a diffuse surface on one of thesheet faces. By using this set of tanks, the vapor pressure ofhydrofluoric acid can be manipulated to decrease attack times on theflat glass sheet. The main disadvantage of this process is that it canbe applied only to one of the two flat glass surfaces, in addition torequiring long times to obtain the desired finish (minimum time 40minutes), whereby scaling this type of batch process to industrial leveldoes not seem to be profitable.

There are other methods not using acids to reduce reflection of lightfrom the surface of flat glass, as described by Cook et al. (U.S. Pat.No. 4,434,191) where the possibility of using electrolyte solutionshaving a dissociation constant greater than 10-6 at a temperature of 20°C. is suggested. This type of method permits treating flat glass byimmersion in electrolyte solutions, which have a neutral pH close to7.0. In particular, by using this method it is possible to generate ahigh quality anti-reflective coating on the surface of flat glass whichcan be used for optical applications. The disadvantage of this method,like those mentioned above, is that it requires very long exposure timesof flat glass to the electrolyte solution. Cook mentions in his workthat normal times to achieve the anti-reflective coating range from12-90 hours. Unfortunately, these times prevent having an industrialproduction unless having extremely large containers, which would involvea very high investment.

Efforts have made to obtain a production process for treating bothsurfaces of glass simultaneously, but undoubtedly the processes closerto achieving the desired goal are those involving immersion of flatglass sheets in acidic solutions.

Per the above, the present application discloses a batch type industrialprocess to produce several diffuse finish sheets of flat glasssimultaneously, reducing considerably the value of reflection ofspecular light allowing applying the obtained product for protection ofphotographs and artwork.

OBJECTIVES OF THE INVENTION

It is therefore a first object of the present invention, to provide aproduction method for sheets of glass with a diffuse finish, andresulting sheet of glass, which allows obtaining a satin and diffusefinish on both surfaces of the glass sheet.

It is another object of the present invention to provide a productionmethod for sheets of glass with a diffuse finish by immersion in acidsolutions, modifying its optical properties and giving them a diffusefinish.

A further object of the present invention is to provide a productionmethod for sheets of glass with a diffuse finish providing a reflectionlevel of about 1%.

Another object of the present invention is to provide a productionmethod for sheets of glass with a diffuse finish, which provides anaverage roughness of 0.8020 μm to 0.7081 μm.

These and other objects and advantages of the manufacturing process ofglass sheets with diffuse finish of the present invention will becomeapparent to those skilled in the art, from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a shows an image of roughness for ATR glass, 3-dimensional, sideone.

FIG. 2 shows a plot of roughness, in one dimension, for ATR glass, sideone.

FIG. 3 shows an image of roughness for ATR glass, 3-dimensional, sidetwo.

FIG. 4 shows a plot of roughness, in one dimension, for ATR glass, sidetwo.

FIG. 5 shows an image of roughness for PAVIA glass, 3-dimensional, sideone.

FIG. 6 shows a plot of roughness, in one dimension, for PAVIA glass,side one.

FIG. 7 shows an image of roughness for PAVIA glass, 3-dimensional, sidetwo.

FIG. 8 shows a plot of roughness, in one dimension, for PAVIA glass,side two.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the manufacturing process of glass sheets comprising thefollowing steps:

a) Providing Flat Glass Plates

For the start of the manufacturing process, packages of flat glass aresupplied, to be processed in groups, which are received in storage racksspecially designed so that the glass does not suffer any damage eitherby scratches or breaks.

b) Immersion of Glass Plates in an Acid Solution

The next step is to introduce at least one glass sheet in a first acidicsolution. Such a solution may be a solution of 32.5% hydrochloric acidfor a time from 20 to 60 seconds, to remove all impurities that may bepresent in the sheets of flat glass such as any remains of separatordust, fingerprint marks, glove stains, etc. This process is carried outin a container that can process from 1 to 7 sheets of minimum size 1200cm by 1800 cm and maximum dimensions of 1800 cm by 2600 cm withthicknesses ranging from 2.0 mm to 19 mm which is equivalent toprocessing from 75.6 kg to 1556.1 kg of glass.

c) Rinsing Glass Sheets.

Once the glass sheet has been subjected to the acidic solution, thesheets are subjected to a washing or rinsing process to remove theremaining acid solution and avoid the formation of lines and undesirablemarks in the flat glass.

d) Immersion of Glass Sheets in a Second Acidic Solution

Once the remains of the first acidic solution (hydrochloric acid) areremoved, the sheet or sheets of glass are subjected to a secondimmersion in a second acidic solution composed of a mixture of 70%ammonium difluoride and 30% hydrochloric acid 32.5% for a period ofbetween 30 seconds and 300 seconds. Immersing the glass sheets in thismixture produces a finish on both sides of the glass sheets but alsoleaves a crust on them, which must be removed.

e) Immersion of Glass Sheet in an Alkaline Solution.

To achieve crust removal, it is necessary to introduce again the glasssheet or sheets in an alkaline solution, such as a 2% solution ofcaustic soda. To facilitate removal of the crust, the caustic solutionis subjected to a stirring by bubbling process, for a time from 2minutes to 5 minutes depending on the degree of crust removal.

f) Flushing Glass Plates

After removing the crust the glass sheet is carried to a second rinsestep and the residual caustic soda solution present in the sheets andcontainer is removed.

g) Immersion of Glass Sheets in an Acidic Solution

The next step is to introduce again one or more sheets of glass in anacidic solution. Said acidic solution may be a solution of 32.5%hydrofluoric acid. The immersion time will be from 30 to 600 seconds.With this immersion, the opacity generated in the previous step can beeliminated, keeping the roughness originated on the surface of theglass, making the glass resume its transparency but with a low level oflight reflection.

h) Immersion of Glass Sheets in an Alkaline Solution.

Once completed the attack time with the 35% hydrofluoric acid solution,the glass sheet or sheets are introduced again in a tank containing asolution of 2% caustic soda. This stage aims to stop the reaction ofhydrofluoric acid with glass. Such glass sheets are kept within the tankfrom 20 seconds to 60 seconds as required.

i) Rinsing and Drying the Glass Sheets

Once the glass sheet was treated with caustic soda, a second step ofrinsing and drying takes place, to remove the residual solution ofcaustic soda present in the sheets and the tank.

Finally, once the product meets the required specifications and quality,it is taken to storage.

Per the above-described process, roughness measurements were made byprofilometry for glass types ATR (anti reflection) and PAVIA® (Trademarkof company Vitro Vidrio y Cristal), on both faces.

All measurements were made under the following conditions:

Swept area: 1.2×1.2 cm with sweeping steps every 1 μm.

Force applied to the sample: 10 mg.

Sweeping speed: 200 μm·s⁻¹

At atmospheric pressure and room temperature.

The results obtained are summarized in Tables 1, 2 and 3. FIGS. 1 to 8show for each measurement, an image of 3D roughness and a graph of theroughness in one dimension.

TABLE 1 Parameters obtained from measurements ATR PAVIA Side 1 side 2Side 1 side 2 PARAMETER (attack) (attack) (attack) (No attack) Roughnesspeak - 5.8343 μm 5.9244 μm 9.3790 μm 0.0641 μm valley (Rt) Roughness0.8020 μm 0.7081 μm 0.9538 μm 0.0091 μm average (Ra) Roughness RMS0.9653 μm 0.8764 μm 1.1917 μm 0.0111 μm

TABLE 2 Optical Properties of Anti-Glare Glass (ATR) Sample R Solar RSolar R light R Light (thickness) T Solar (Front) (Back) T light (Front)(Back) T UV 2.0 ATR 84.8% 7.4% 7.3% 88.5% 7.8% 7.7% 64.2% Color T ColorRDP Color RDV Sample L* a* b* L* a* b* L* a* b* 2.0 ATR 95.353 −0.6980.256 33.515 −0.585 −0.347 33.345 −0.582 −0.231 T Solar: Solartransmission; R Solar: Solar reflection; T light: Light Transmission; RLight: Light reflection

TABLE 3 Optical Properties of PAVIA Anti-Glare Glass Sample R Solar RSolar R light R Light (thickness) T Solar (Front) (Back) T light (Front)(Back) T UV 3.0 PAVIA 82.60% 6.00% 6.00% 88.60% 6.50% 6.50% 70.20%Sample R Solar R Solar R light R Light (thickness) T Solar (Front)(Back) T light (Front) (Back) T UV 6.0 PAVIA 74.10% 5.50% 5.50% 84.50%6.20% 6.20% 59.60% Color T Color RDP Color RDV (Color to (Color toreflection (Color to reflection Color T Color RDP Color RDV Sample L* a*b* L* a* b* L* a* b*

Sample R Solar R Solar R light R Light (thickness) T Solar (Front)(Back) T light (Front) (Back) T UV 12.0 PAVIA 59.10% 4.80% 4.80% 76.10%5.70% 5.70% 45.70% 1 Color T Color RDP Color RDV Sample L* a* b* L* a*b* L* a* b* 12.0 PAVIA 89.98 0.249 0.662 28.66 4.47 10.86 28.66 4.4710.86 Sample R Solar R Solar R light R Light (thickness) T Solar (Front)(Back) T light (Front) (Back) T UV 19.0 PAVIA 46.50% 4.40% 4.40% 67.70%5.20% 5.20% 35.60% 1 Color T Color RDP Color RDV Sample L* a* b* L* a*b* L* a* b* 19.0 PAVIA 85.94 0.351 0.953 27.64 4.64 11.33 27.46 4.6411.33

indicates data missing or illegible when filed

From the above, a manufacturing process has been described tomanufacture a diffuse glass and a resulting glass and it will beapparent to those skilled in the art that other possible advances orimprovements can be performed, which may be considered within the fielddetermined by the following claims.

1. A glass sheet with diffuse finish produced by the process of: a)Providing a sheet of glass; b) Providing a first immersion of the glasssheet in a first acidic solution for a predetermined time, to removeimpurities from the glass; c) Rinsing or washing the glass sheet once ithas been immersed in the first acidic solution to remove the remainingacidic solution and avoid the formation of undesirable lines and marksin the glass; and d) Providing a second immersion step to said glasssheet in a second acidic solution for a second predetermined time togenerate a diffuse finish on both sides of the glass, wherein theprocess generates in the glass sheet, on at least one side, a diffusesurface with a peak-valley roughness (Rt) from 5.8343 μm to 9.3790 μm;an average roughness (Ra) between 0.8020 μm and 0.9538 μm; RMS roughnessbetween 0.9653 μm and 1.19167 μm; a solar transmission between 84.8% and46.50%; a solar reflection between 7.4 and 4.4%; a light transmissionbetween 88.5% and 67.70%; a reflection of light between 6.50% and 5.20%;and UV transmission between 35.60% and 70.20%.
 2. The glass sheet withdiffuse finish produced by the process of claim 1, including theadditional steps of: e) Providing a third step of immersing the glasssheet from step d) in an alkaline solution for a third predeterminedperiod; and f) Rinsing or washing the glass sheet to remove any residualalkaline solution from the glass sheet.
 3. The glass sheet with diffusefinish produced by the process of claim 2, including the additionalsteps of: g) Providing a fourth immersion step to said glass sheet in athird acidic solution for a fourth predetermined period; h) Providing afifth step of immersing the glass sheet from step g) in the alkalinesolution of step e) to stop the reaction of the third acidic solution insaid glass sheet; and i) Rinsing the glass sheet to remove residues ofthe alkaline solution.
 4. The glass sheet with diffuse finish producedby the process of claim 1, wherein the first acidic solution is ahydrochloric acid solution of 32.5% hydrochloric acid by volume.
 5. Theglass sheet with diffuse finish produced by the process of claim 1,wherein the second acidic solution is a mixture of 70% ammoniumdifluoride and 30% of 32.5% hydrochloric acid by volume.
 6. A glasssheet with diffuse finish produced by the process of: a) Providing asheet of glass; b) Providing a first immersion of the glass sheet in afirst acidic solution for a predetermined time, to remove impuritiesfrom the glass; c) Rinsing or washing the glass sheet once it has beenimmersed in the first acidic solution to remove the remaining acidicsolution and avoid the formation of undesirable lines and marks in theglass; and d) Providing a second immersion step to said glass sheet in asecond acidic solution for a second predetermined time to generate adiffuse finish on both sides of the glass, wherein the process generatesin the glass sheet, in at least one side, a diffuse surface comprising:a peak-valley roughness (Rt) of about 5.9244 μm; an Ra roughness ofabout 0.7081 μm; an RMS roughness of about 0.8764 μm; a solartransmission of at least 84%; a solar reflectance of about 7.3%; a lighttransmission of about 88.5%; and UV transmission of about 64.2%.
 7. Theglass sheet with diffuse finish produced by the process of claim 6,including the additional steps of: e) Providing a third step ofimmersing the glass sheet from step d) in an alkaline solution for athird predetermined period; and f) Rinsing or washing the glass sheet toremove any residual alkaline solution from the glass sheet.
 8. The glasssheet with diffuse finish produced by the process of claim 7, includingthe additional steps of: g) Providing a fourth immersion step to saidglass sheet in a third acidic solution for a fourth predeterminedperiod; h) Providing a fifth step of immersing the glass sheet from stepg) in the alkaline solution of step e) to stop the reaction of the thirdacidic solution in said glass sheet; and i) Rinsing the glass sheet toremove residues of the alkaline solution.
 9. The glass sheet withdiffuse finish produced by the process of claim 6, wherein the firstacidic solution is a hydrochloric acid solution of 32.5% hydrochloricacid by volume.
 10. The glass sheet with diffuse finish produced by theprocess of claim 6, wherein the second acidic solution is a mixture of70% ammonium difluoride and 30% of 32.5% hydrochloric acid by volume.11. A glass sheet with diffuse finish produced by the process of: a)Providing a sheet of glass; b) Providing a first immersion of the glasssheet in a first acidic solution for a predetermined time, to removeimpurities from the glass; c) Rinsing or washing the glass sheet once ithas been immersed in the first acidic solution to remove the remainingacidic solution and avoid the formation of undesirable lines and marksin the glass; and d) Providing a second immersion step to said glasssheet in a second acidic solution for a second predetermined time togenerate a diffuse finish on both sides of the glass, wherein theprocess includes in the glass sheet, in at least one side, a diffusesurface without attack, comprising: one peak-valley roughness (Rt) ofabout 0.0641 μm; an Ra roughness of about 0.0091 μm; and an RMSroughness of about 0.0111 μm.
 12. The glass sheet with diffuse finishproduced by the process of claim 1, including the additional steps of:e) Providing a third step of immersing the glass sheet from step d) inan alkaline solution for a third predetermined period; and f) Rinsing orwashing the glass sheet to remove any residual alkaline solution fromthe glass sheet.
 13. The glass sheet with diffuse finish produced by theprocess of claim 12, including the additional steps of: g) Providing afourth immersion step to said glass sheet in a third acidic solution fora fourth predetermined period; h) Providing a fifth step of immersingthe glass sheet from step g) in the alkaline solution of step e) to stopthe reaction of the third acidic solution in said glass sheet; and i)Rinsing the glass sheet to remove residues of the alkaline solution. 14.The glass sheet with diffuse finish produced by the process of claim 11,wherein the first acidic solution is a hydrochloric acid solution of32.5% hydrochloric acid by volume.
 15. The glass sheet with diffusefinish produced by the process of claim 11, wherein the second acidicsolution is a mixture of 70% ammonium difluoride and 30% of 32.5%hydrochloric acid by volume.